This invention relates to jet printers, including jet printers for direct-to-plate printing systems.
Ink-jet printers operate by charging drops of ink with a charging electrode and guiding them to a print substrate through a high intensity electric field. Printers can modulate the charge on an ink drop by changing the charging electrode voltage to select whether each drop is to be printed or instead sent to a gutter. Printers may also adjust the charging voltage to compensate for aerodynamic effects and for the influence of the charge from adjacent drops. Some printers employ a technique known as xe2x80x9cswathingxe2x80x9d to continuously change the field and thereby direct drops from one or more stationary ink jets to different locations on the printing substrate, instead of moving a print head across the substrate.
Jet printing techniques are applicable to direct-to-plate printers. Such printers typically apply a printing fluid to a sheet of plate stock mounted on a drum. This fluid causes changes in the portions of the surface of the plate on which it is deposited. Although further processing of the plate may be necessary, the result is a printing plate that can serve to print large numbers of pages.
In one general aspect, the invention features a jet printer that includes a drum constructed and adapted to receive a print substrate and a drum control interface having an output provided to a motor for rotating the drum. The printer also includes a print head with a first jet printing fluid source attached to a movable carriage and at least one deflection element located proximate an output trajectory of the first jet printing fluid source. The deflection element has a deflection axis in the direction of an axis of rotation of the drum. Further included are a carriage mechanism for moving the carriage in the direction of the axis of rotation of the drum, a swathing table, interleaving logic with an output provided to the print head, and a control circuit responsive to the swathing table and having an output provided to at least the one deflection element.
In preferred embodiments, the print head can further include a second jet printing fluid source attached to the carriage, with the interleaving logic being operative to provide interleaved portions of data to be printed by the first and second jet printing fluid sources. The interleaving logic can include horizontal and/or vertical interleaving logic. The printer can further include a processor portion operative to drive the printer to print half-tone images on a print substrate. The print substrate can be a printing plate. The deflection element can be a charging tunnel surrounding an output of the jet printing fluid source. The deflection element can be one of a pair of deflection electrodes. The swathing table can include a series of different firing order entries that define different deflection amounts for the deflection element, whereby the deflection element directs drops from the printing fluid source to a succession of different locations on the printing substrate.
In another general aspect, the invention features a method of jet printing that includes moving a first jet printing fluid source relative to a print substrate along the direction of an axis of rotation of a print substrate. A first drop of printing fluid from the jet printing fluid source is electromagnetically guided so that it lands on the print substrate at a first distance along the direction of the axis of rotation of the print substrate from the jet printing source and at a first distance along the direction of advance of the print substrate. A second drop of printing fluid from the jet printing fluid source is electromagnetically guided so that it lands on the print substrate at a second distance along the direction of the axis of rotation of the print substrate from the jet printing source, with the first and second distances being different The method also includes rotating the print substrate relative to the jet printing fluid source about the axis of rotation after the step of electromagnetically guiding a first drop to advance the print substrate, and depositing a third drop adjacent the first drop after the step of rotating and according to an interleaved print pattern.
In preferred embodiments, the step of depositing can include depositing the third drop by a second jet printing fluid source between the-first and second drops in the direction of the axis of rotation of the print substrate. The step of depositing can include depositing the third drop by the first jet printing fluid source between the first and second drops in the direction of the axis of rotation of the print substrate, with the deposition of the first and third drops being separated in time by at least about a full revolution of the drum. The step of depositing can include depositing the third drop adjacent the first drop by a second jet printing fluid source at a second distance along the direction of advance of the print substrate, with the first and second distances along the direction of advance of the print substrate being different. The step of depositing can include depositing the third drop adjacent the first drop by the first jet printing fluid source at a second distance along the direction of advance of the print substrate, with the first and second distances along the direction of advance of the print substrate being different, and with the deposition of the first and third drops being separated in time by at least about a full revolution of the drum. The steps of moving, guiding, rotating, and depositing can form a part of a half-tone printing process and/or can be performed using a printing plate as a substrate.
In a further general aspect, the invention features a jet printer that includes means for moving a jet printing fluid source relative to a print substrate along a direction of an axis of rotation of a print substrate, means for rotating the print substrate relative to the jet printing fluid source about the axis of rotation to advance the print substrate, means for electromagnetically guiding a first drop of printing fluid from the jet printing fluid source so that it lands on the print substrate at a first distance along the direction of the axis of rotation of the print substrate from the jet printing source and at a first distance along the direction of advance of the print substrate, and for electromagnetically guiding a second drop of printing fluid from the jet printing fluid source so that it lands on the print substrate at a second distance along the direction of the axis of rotation of the print substrate from the jet printing source, wherein the second distance is different from the first distance, and means for causing a third drop to be deposited adjacent the first drop after the drum has rotated and according to an interleaved print pattern.
In preferred embodiments, the means for causing can include means for causing the third drop to be deposited by a second jet printing fluid source between the first and second distances in the direction of the axis of rotation of the print substrate. The means for causing can include means for causing the third drop to be deposited by the first jet printing fluid source between the first and second drops in the direction of the axis of rotation of the print substrate, with the deposition of the first and third drops being separated in time by at least about a full revolution of the drum. The means for causing can include means for causing the third drop to be deposited adjacent the first drop by a second jet printing fluid source at a second distance along the direction of advance of the print substrate, with the first and second distances along the direction of advance of the print substrate being different. The means for causing can include means for causing the third drop to be deposited adjacent the first drop by the first jet printing fluid source at a second distance along the direction of advance of the print substrate, with the first and second distances along the direction of advance of the print substrate being different, and with the deposition of the first and third drops being separated in time by at least about a full revolution of the drum. The printer can include means for driving the printer to print half-tone images on a print substrate. The print substrate can be a printing plate.
Systems according to the invention can be advantageous in that they provide an inexpensive, accurate and flexible method of controlling the trajectory of drops of printing fluid in jet printing. By treating drops as samples in a sampled-data system, printers can perform swathing, aerodynamic compensation, and adjacent drop compensation in the digital domain using an existing printer control processor or an inexpensive add-on microprocessor. Such printers can also be reconfigured for different printing applications without requiring a redesigned analog circuit, and they may even be digitally calibrated at start-up or on-the-fly to improve print characteristics. These features can improve the quality of printing, and can reduce the cost and time involved in developing improved printers.
Systems according to the invention may also permit printing operations to take place more quickly and efficiently, in moving-head, direct-to-plate, jet printers. Swathing can permit such printers to deposit individual charged drops that are spaced apart in two polar dimensions on a plate as it rotates. And interleaving can increase drop spacing as well. This allows for fine-pitch printing at high speeds with a minimum number of guard drops.